(1) Field of the Invention
The present invention relates to an apparatus for measuring bubble or drop velocity and its diameter etc. in liquid-gas two-phase flow simultaneously.
(2) Prior Art
Several type of apparatuses for measuring bubble velocity and its diameter in liquid-gas two-phase flow have already been proposed. One of them is an apparatus for measuring changes of electric resistance in the two-phase flow. The apparatus has a sensing part which comprises a pair electrodes. They consist of a minute point electrode provided at the point of a needle like metal line coated by an insulator, and a fine metal duct wrapping the coated metal line except the point part. A predetermined voltage is applied across the pair of electrodes, and the sensing part is placed in the liquid-gas two-phase flow. In case the sensing part is in a liquid phase, the resistance between the two electrodes becomes a specified value determined by the nature of the liquid. But if the point electrode is in a gas phase, the two electrodes are almost insulated, that is to say the resistance becomes an extremely large value. Therefore, the state of the liquid-gas two-phase flow can be measured by detecting the change of the resistance value of the flow. However, the method of this type is effective only when the liquid is conductive. And if the liquid is non-conductive liquid, such as oil or alchol, the flow containing such liquid cannot be measured since the electrodes of the sensing part are always insulated from each other. But, even if the liquid is conductive, in case there is a possibility that chemical change occurs in the liquid by current flow arising from voltage application, it is improper to measure the two-phase flow by this conventional appratus.
Another conventional measuring apparatus has an optical fiber bent to an U-shaped and taken off its coating as a sensing part. Light is guided into one end of the optical fiber placed in the liquid-gas two-phase flow. When the sensing part is in the liquid phase, a part of the fed light leaks into the liquid since the difference between the refraction indices of the liquid and the fiber (glass) is very small, and thus the output light intensity from the other end of the optical fiber decreases. On the other hand, when the sensing part is in the gas phase, namely it is in a bubble, the fed light does not leak to the bubble since the light is totally reflected by the boundary face of the fiber and the bubble, and thus the output light intensity from the other end of the fiber does not decrease. Therefore, the liquid-gas two-phase flow can be measured by detecting the change of the output light intensity. However, in this method, it is very difficult to minimize the sensing part because the sensing part is the U-shaped fiber. Accordingly this measuring apparatus can not detect small bubbles, and high measuring reliability cannot be expected.